1. Field of the Invention
The present invention relates to a display unit with touch panel for use in operation devices such as employed by FA (factory automation) apparatuses, vending machines, automatic ticket venders, information apparatuses, household electrical appliances, medical instruments and the like.
2. Description of the Background Art
Conventional display units with touch panels are constructed as shown in FIG. 1. The display units are used in the operation stations of the FA (factory automation) apparatuses or in the operation switch portions of the vending machines, automatic ticket venders, information apparatuses, household electrical appliances, medical instruments and the like.
Such a display unit with touch panel has a construction wherein a touch panel 102 is fixed at place above and close to a display body 101 with a display screen for displaying image information including characters, patterns, symbols and the like, based on image data outputted from an image data output device such a computer.
A typical example of the display body 101 is composed of a liquid crystal display.
The touch panel 102 includes a plurality of switch portions (m.times.n) arranged in a matrix of M-rows and N-columns (hereinafter, M and N each indicate an integer of not smaller than 1) in the XY directions perpendicular to each other. These switch portions feature a substantially zero depression stroke such that an operator can operate the switch portions by lightly touch or press them. The touch panel 102 outputs two types of signals for indication of an operated position, which signals include an n-component positional signal XS (n=1, . . . , N) indicative of the position on the X-axis and an m-component positional signal YS (m=1, . . . , M) indicative of the position on the Y-axis. The touch panel 102 is formed of a transparent or translucent material for allowing light from the display body 101 therebelow to pass therethrough. A typical example of the touch panel 102 is of a resistance type.
The component positional signals XS and YS from the touch panel 102 are supplied to an operated-position detecting circuit 103. The operated-position detecting circuit 103, in turn, detects coordinates (Xn, Ym) of an operated position on the touch panel 102 based on the component positional signals XS and YS and then outputs an operated-position signal PS indicative of the operated position on the panel. Thus, the position at which the touch panel 102 is operated can be determined from the operated-position signal PS.
The touch panel 102 of the construction shown in FIG. 11 allows for the minimization of the thickness thereof and offers a high degree of freedom to define a region practically used as switch. Unfortunately, however, the touch panel is adapted to respond to an impact no stronger than an operator's light touch on the switch portion of the touch panel 102. This leads to a fear that when the operator accidentally touches the surface of the touch panel 102 or merely traces switches on the touch panel 102 for confirmation of display content or such, an operated-position signal PS indicative of a position at which the operator has touched the touch panel 102 may be supplied from the operated-position detecting circuit 103 to a subsequent circuit, resulting in an operation error of a subsequent external device due to the mistake of the operator. Particularly, in the case of a production line of a factory where the operation station for controlling the production process is equipped with such a display unit with touch panel, the operator normally pays his attention solely to the movement of the production line but not so far as to what portion of the touch panel he touches. Hence, the operation error is apt to occur.
In the case of the construction shown in FIG. 11, the touch panel 102 does not allow the operator to depress the switch portion thereof so that the operator cannot obtain any tactile-response to the operation of the switch portion. That is, the touch panel 102 cannot give a tactile feedback to the operator when responding to the operation of the switch portion thereof.
Similarly to the resistance type touch panel, the aforementioned problem also exists with the touch panel 102 of other types such as ultrasonic type, photoelectric type, capacitance type and the like.
In the case of the photoelectric type touch panel, in particular, a light emitting device emit light beams in a matrix pattern at a level slightly away from the surface of the touch panel 102 to be touched by the operator and therefore, some of the light beams from the light emitting device are cut off by an operator's finger before the operator actually touches the surface of the touch panel 102. This results in a trouble that although the operator does not touch the touch panel 102, the operated-position detecting circuit 103 supplies to a subsequent external device an operated-position signal PS indicative of a position corresponding to where the light beams are cut off.